This invention relates to an ion gauge system and more particularly to an ion gauge providing a digital display operative over a pressure range of several decades.
In most ion gauge systems presently available, the ion current is measured by conventional analog techniques and, if a digital display is desired, the resultant analog voltage is then converted to a digital representation by conventional means, e.g. dual slope integration, voltmeter circuits, etc. In order to provide for range changing, the analog circuitry in such prior art systems has typically employed the switching in of resistors of different values so as to scale the output signal, the switching being either manual or automatic under the control of analog out-of-range detectors. If a digital display is then driven by the analog display, its scale factor must be switched in correspondence with the changing of the analog scale factor. As will be understood by those skilled in the art, such an approach leads to considerable complexity together with substantial cost owing to the need for a plurality of high-value precision resistors as well as elaborate sensing switching circuitry.
Among the several objects of the present invention may be noted the provision of an ion gauge system in which ion current is directly measured by a method appropriate for digital scaling and display; the provision of such a system which will operate over a pressure range of several decades without elaborate analog out-of-range detection; the provision of such a system which is highly accurate and highly reliable and which is of relatively simple and inexpensive construction. Other objects and features will be in part apparent and in part pointed out hereinafter.